Method and apparatus for renewing targets



June 28, 1960 c. GOODMAN 2,943,239

METHOD AND APPARATUS FOR RENEWING TARGETS Filed June 29, 1954 POWERSUPPLY HIGH VOLTAGE POWER SUPPLY INVENTOR. CLARK GOODMAN BY W/J msATTORNEY su h,as,ttitium,: T will be-described in this connection. 7 V

.Egrpcrience neutron generators of thetoregoing" @ype as ndicatedIhatJ't-he neutron yield may not always rrruahbe replaced frequently. a

To replace the target, the accelerator mustfirstbe disasscmbledyandthedepletedtarget removed. Anew 2,943,239 1 METHOD an TUs For: neunwmeTARGETS can Goodman, Boston, Mass, assignor, by mesne assignments, toSchlumhergerWell Surveying Corpora- -'t1on, Houston,;Tex., a corporationof Texas mus-u June 29, 1,954, "ser. No. 440,229 is Claims. (cl.315-111) invention relates to methods and apparatus-tor renewing-targetsand, more particularly, pertains to new and improved. methods andapparatus for conditioning a target element of a particle acceleratorwith a selected Ihemcthdds and apparatus for renewing targets em-;bodyingdhe ipresentinvention may have utility in a var ety ofapplications. .However, it is ideally suited for 41s ginyassociationwith a particle accelerator intended 91 highly zaccelfi ted dcnteriumions and a target material,

conv ience, the present invention J the gcneration t t-neutrons throughreactions between maintained .atr-agdesired high level because a ofdeplejtlonofi tritium ,inthe, target. Consequently, the target target isprepared, according to: present techniques, by hydridiugyalayer 'Qfzirconium metal mounted on a tungsten backing with deuterium or tritium,as the .case .may be. The accelerator'is then reassembled with the newtarget; however, in this last step of the process itis notpossible toheat the device above approximately 400? United States m 9 C.withoutundue loss of the valuable isotope of hydrogen.

.This severely. limits the eificiency of the out-gassing process andtheoperation of the acceleratormay be impaired by undesirablecontaminants. I

FurtheImore experience has indicated .that targets (w ich, have beenexposed, to the atmosphere after hy'dpften develop a nomhydrided surfacelayer (prespmablyrdue to oxidation) This surface layer may be,dleuterons-pf 10D kilovolts;-energy. Accordingly, it is necessarytoacceleratet he deuterons through .120 to 130 lcilovolts inorder toobtain a resultant energy' of: 100 kilovolts (at; which maximum neutronyieldoccurs) for bombardmenflof the underlying hydride layer; after thedeuteron's have penetrated the surface layer. In many applications ofthe accelerator, ,this additional. voltage nqqbe readily attainable.

. It is,-therefore,. an objectof the present invention to provide new;and improved methods and apparatus for renewing-Such targets withoutdisassembling the .accele- Another object; ofthe pre'sent invention isto provtde new ,and improvedmethods. andappa'ratus for hydridlng heo'rder of 20,000, toL.30,0(:)0 electron volts thick for .ing. material,such as out-gassed glass.

2,943,239 Patented June 28, l 960 roe temperature of the gas absorbentelement to a value at which the selected gas may be absorbed.Thereafter, the temperature of the gas-absorbent element is reducedbelow the aforesaid value and excess gas is removedfrom the envelope; vI

According to another aspect of the present invention, there is providedapparatus .for carrying out the abovedescribed method. This apparatusmay be employed in combination with an element of a particle accelerator.havingan envelope and comprises a gas-storing mechanism incommunication with the envelope. The gasstoring mechanism hasgas-emitting and gas-absorbing operating conditions. The apparatusfurther comprises control meansfor selectively establishingthegas-emitting operating condition in the mechanism to introduce gasinto the envelope and means are providedfor conditioning the element toabsorb gas. .'Ihe control. means may also be employed for selectivelyestablishing the gas-absorbing operating conditionso as to absorb excessgas from the envelope. t 1 p p .Ihe novel features of the presentinvention; are set forth with. particularity in the appended claims. The

present invention, both as toits organization and manpar of operation,together with furtherobjects and advantagesthereof, may best; beunderstood by reference to the following description taken in jconnection ,with

Th e m in d a in, ,Wfi t messi a ess se v swi a -m ieelgi rs s st en twards ea T QPFq PP 333 are: method ihs e is. e present invention andillustrating novel. apparatus com structed in accordance with theinvention. 2

As shown in the drawing, a recqnditionings tem constructedin accordancewith the present invent ioir is; embodied in a particle acceleratorwhich comprises .an

evacuated envelope 10 composed of an electrical insulat- V nv j e 19 isevacuated, and as will he described hereinaften is; filled withionizable gas, such as an isotope oi l hydrogen known as deuterium, at aselected pressure .of l to=10 microns ofmercury. H k t l r, I

To derive ions of the gas within envelope it), there is provided an ionsource l'linc'luding a tubular .Orcylin- .dric'al anodelZ and a pairofcathode plates, i3' and 14 supported at opposite ends or cylinder l2. jConnections from a medium voltage-power supply 15 to clement; 12- 14 ofion source 11 arefcompleted over leads which. are

suitably sealed in respective openingsin envelope 10in a: known manner.A cylindrical magnet jle' receives envelope 10 and'is essentiallycoextensive withlanode cylin der 12. The, ion source just describedisdisclosed in the ,copendin-g. application of John 'l. Dewan, filed April9,

.1952, bearing the Serim No. 281,378-andassigi1edzto the sameassignee'asthe presenti-nvention 1.1} Some of mo ions which are deiived insource1.1 may pass through an opening 17 in cathode plate 14 and are therebyintroduced to an accelerating gap 18 via an opening 19 of a probeelectrode Zi) included in the etothe at an accelerator irrsitu either inan initial stepoflan assembly process or as a step' in the process suaset enmime. l j

'-A method embodying the-present inventionmay be em I t', a j g'asabsorbnt element of a particle particle accelerator and increasing theed with an envelope. The method ,comof introducing a [selected gas intothe ofjrenewingithe hydridela'yer as maybe required at any 23,constructed of a metal having a, thermal coefficient' oi expansionsimilar to .that of glass envelope 19,. such as an alloy of nickel,cobalt, manganesc and iron, com monly referred to as Kevan Cylinder 23's" suitably fused or sealed to the periphery of an opening 24 in thelower end of envelope 10 and its upper end is closed by a tungstenbacking plate 25 suitably attached thereto,

1 such as by silver soldering techniques.

Backing plate 25 may be of planar construction'or ;may be of thealternate construction shown in the copending application of ClarkGoodman, filed May 26, -l954, bearing the Serial No. 432,345 andassigned to the same assignee as the present invention. According to thealternate construction, backing plate 25 may be deformed so as tocomprise a plurality of concentric corrugations.

The upper surface of backing plate 25 is covered in its entirety by atarget element 26 which may be composed of a layer of a materialabsorbent to tritium, such as zirconium. Layer 26 is made thin in orderto mini- 'mize the amount of tritium required but is sutficiently thickto permit accelerated particles to react completely with tritium gaswhich may be absorbed thereby during a process in accordance with thepresent invention, as will be more fully described hereinafter. Layer26, for example, may be 1 to 10 microns in thickness and preferablyshould be adapted to form a stable hydride at a temperature occurringunder normal operating conditions of the accelerator. Moreover, itshould be fusable to the metal of backing plate 25 and should not flakeoff when hydrided with the selected isotope of hydrogen.

Element 26 is selectively absorbent to tritium at certain temperatureswithin a range from 400 to 600 C. This temperature may be obtained bymeans of a heater coil-27 located adjacent to, butelectrically insulatedfrom, the lower surface of backing plate 25. For example, coil "27 maybea flatspiral separated from plate 25 'by a thin mica disc.

One end of coil '27 is connected to the inner surface of cylinder 23 andits other end 'cxtendsthrough an insulating sleeve 28 at the lower end'of cylinder 23. Coil 27 may be energized by a battery 29 which may beselectively connected thereto via an "operating switch 30.

shaped exterior adapted to cooperate with a ground glass seat 35 at theupper end of chamber 33. The valve element 34 is connected'to a softiron actuator or armature 36, preferably enclosed by a glass layer 37. Aquartz compression spring 38 disposed between the lower end of actuator36 and a shoulder 39 formed by the junction between tube 32 and valvechamber 33 normally 'forces the valve into its closed position.

To open the valve, there is provided a solenoid 40 which receives valvechamber 33. The solenoid is supported adjacent armature 36 and may beselectively energized by a battery 41 via an operating switch 42.

The upper end of valve chamber 33 is connected by an integral tube 43 toa heater chamber 44. The upper end of the heater chamber is closed by aseal 45 through which sealed leads pass so that connections may beintroduced to a heater or filament 46. Filament 46 may be comprised of athin zirconium wire spirally wound on a supporting wire of'tungsten.Alternatively, a wire core constructed of molybdenum, stainless steel,'or oxide coated steel may support a pair of wires wound in parallel,interspersed relation to one another. One of the latter wires may becomposed of tungsten or molybdenum whereas the other wire may becomposed of zirconium'as disclosed in the copending application ofArthur H. Frentrop, filed March 8, 1954, bearing the Serial No. 414,839and assigned to the same assignee as the present invention.

Heater 46 is hydrided with deuterium gas in a known manner and maybe-energized by a battery 47"via an operating switch 48'. A variableresistor 49 is provided so that filament 46 may be raised selectively toits deuterium-absorbing temperature in a range from 300 to 600 C. or toits deuterium-emitting temperature in a range from 600 to 800 C. Ofcourse, the emitting and absorbing temperatures are dependent on the gaspressure within the closed system including envelope 10 and gas-storingmechanism 31 and thus the required temperatures may be selected in aknown manner.

The reconditioning system embodying the present invention furthercomprises a second gas-storing 'mechanism 50 which may be of aconstruction identical to mechanism 31. Mechanism 50 is in communicationwith envelope 10 via a tube 51 and is provided with a valve 52 normallybiased against a seat 53 by a quartz spring 54. Its armature 55 is underthe influence of a solenoid 56 which may be energized by battery 57 viaan operating switch 58. As in mechanism 31, a zirconium filament 59 maybe energized by a battery 60 via an operating switch 61 and a rheostat62 is provided to control the operating temperature of filament 59.However, filament 59 is hydrided with tritium.

In constructing the accelerator shown in the drawing, target assembly 21is sealed into glass envelope 10 before mechanisms 31 and 50 areattached and the assembly is thoroughly out-gassed in a known manner.Thereafter, tubes 32 and 51 are suitably fused to envelope 10 in anatmosphere of argon, the temperature of mechanisms 31 and 50'beingmaintained below approximately 300 C.

"during this procedure, and the envelope is evacuated and sealed.

To hydride target layer 26 with tritiurn,'switch 58 is closed therebyenergizing solenoid 56 and under the in- -fiuence of the magnetic fieldof thesolenoid, armature 55 movesdownwardly thereby opening valve 5253.During this operation, valve 3435 is maintained closed by spring 38.

Switch 61 is then closed and rheostat 62 adjusted so that filament 59 isheated to a temperature in a range from 600 to 800 C. at which tritiumgas is released. The gas flows through the open valve 52-53, through theconvolutions of spring 54- and through tube 51 into envelope 10.

Switch 30 is then closed so that heater 27 may be energized by battery29 and backing plate 25, together with layer 26, is raised to atemperature in a range from 400 to 600 C. at which layer 26 readilyabsorbs tritium.

Accordingly, layer 26 is hydrided and switch 30 is then opened. Toabsorb excess tritium from envelope 10, rheostat 62 is adjusted so thatfilament 59 is reduced to 'a temperature in a range from 300 to 600C. atwhich 'it absorbs tritium. After a suitable interval of-time in whichall the tritium is absorbed, except for that retained by target layer26, switch 61 is opened. Finally, switch 58 is opened, thereby closingvalve 5253.

In order to introduce deuterium gas into envelope 10, switch 42 isclosed and battery 41 energizes solenoid 40. Thus, armature 36 is drawndownward to open valve operates in the manner described in theabove-mentioned V Dewan application and the deuterium gas within the ionsource is ionized. Some of the derived positive-ions drift towardcathode 14 and pass through opening17. Since probe 20 is slightlynegative relative to cathode 14, ions are attracted toward the probe.Some pass through opening 19 and are thus exposed to the eats-ass levelin the neighborhood of 14 million electron volts.

. As the particle accelerator continues to operate and deplete thetritium contained bylayer 26, the ,neutron yield falls ofi. This may beindicated by a suitable detector responsive to the neutron outputoigheparticle accelerator.

15 ad "22 are de-energized' and switches 42 and 48 are closed. Rheostat'49 is adjusted so that filament 46 attains a deuterium-absorbingtemperature and in this manner the pressure of deuterium within envelopeis reduced below the normal operating level. When the pressure has beensufliciently reduced, switches 42 and 48 are opened.

Tritium is then introduced to envelope 10 by closingswitches 58 and 61and layer 26 is heated to tritiumabsorbing temperature by closing switch30, in the manner described hereinbefore. After replenishment withtritium, switches 30, 58 and 61 are opened and switches 42 and 48 areclosed. The latter switches permit the reintroduction of deuterium gasfrom filament 46 in the manner described hereinbefore.

In the final step of reconditioning, switches ,42 and 48 are opened andthepower supplies and 22 may again be energized. l 7

It is thus evident thatthe method and apparatus in d accordance with thepresent invention permits the renewal or replenishment of the targetelement in a particle ac celerator' to be accomplished in situ and thatthe accelerator need not be disassembled for this purpose.

This desirable feature permits the accelerator tube to be sealed oil andmountedwithin apparatus designed for operation remote from controlequipment. For example, it is suited to the requirementsof apparatusadapted to traverse a borehole, such as described in detail in thecopending application of Clark Goodman, filed March 11, 1952, bearingthe Serial No. 275,932 and assigned to the same assignee .as the presentinvention. In'such an environment, long continuous operation at constantneutron intensity'is desirable and thus, after one or more logging runs,the method of target reconditioning embodying the present invention maybe carried out at the surface of the earth. Thus, power for filaments 46and 59, heater 27, and the various valve operators need not be suppliedover the logging cable. The proper external connections may be madeafterthe equipment has returned to the surface.

Although the present invention has been shown inassociation with aspecific type of particle accelerator, it is evident that the method andapparatus may be employed in connection with reconditioning the targetof any of a variety of accelerators. Accordingly, for any otherapplication, tubes 32 and 51 of mechanisms 31 and 50 may be 'celeratorhaving an envelope, a reconditioning system' .for said elementcomprising; a gas-storing mechanism in communication with. said envelopehaving gas-emitting and gas-absorbingoperating conditions; a controlvalve .for interrupting gas communication between said mechanism andsaid envelope; means for selectivelyopcrating said control valve toestablish gas communica- -10 In order-to replenishthe targetlayer, powersupplies 6 tion between said mechanism and-saidenvelope; means forconditioning said element to absorb'g as; and-means for selectivelyestablishing said gas-emitting operating condition in said mechanism, tointroduce gas 'intosa'id envelope for absorption in said element and forselectively establishing said gas-absorbing; operating condition'in saidmechanism to absorb excess gasfirom said envelope.

2.In combination with an element-oi a, ;particle ac :celerator having anenvelope, a reconditioningsystem for said element comprising:- agas-storingmechanism having gas-emitting and gas-absorbing operatingconditions; means for fluidly connecting said mechanism with saidenvelope including a tubular valve chamber; a control valve disposedwithin said chamber and including a valve seat and a member movabletoward said valve seat for interrupting gas communication between saidmechanism and said envelope, at least a portion of said member beingconstructed of a magnetic material; a solenoid enclosing a portion ofsaid valve chamber; means for selectively energizing said solenoid toestablish a magnetic field and displace said member thereby to operatesaid control valve; means for conditioning said element to absorb gas;means for selectively establishing said gas-emitting operating conditionin said mechanism to introduce gas into said envelope for absorption insaid 3. In combination with an element of a particle ac-.

celerator havingan envelope containing afirst, gas, a system forreconditioning said element with a second gas comprising: first andsecond gas-storing mechanisms in communication with said-envelope havinggas-emitting and gas-absorbing operating conditions and individuallycontaining one of said first and second gases; means for selectivelyestablishing said gas-absorbing operating condition in said firstmechanism to absorb said first gas and for selectively establishing saidgas-emitting operating condition to admit said first gas to saidenvelope; means for conditioning said element to absorb gas; and meansfor selectively establishing said gas-emitting o1 crating condition insaid second mechanism to introduce said second gas into'said envelopefor absorption in said element and for selectively establishing saidgas-absorbing operating condition in said mechanism to absorb excessamounts of said second gas firom said envelope.

4. A method of treating an element having a temperature-dependentabsorbing characteristic for a'selected gas in a particle acceleratorhaving an envelope containing one gas at a given operating pressurewhich comprises the steps of: reducing the'pressure of said one gaswithin said envelope below said given operating pressure;

. suitably connected to the envelope of the accelerator and 1 the targetlayer is provided with a suitable backing memintroducing said selectedgas to said envelope of said particle accelerator; increasingthetemperature of said element to a value 'at which said selected gasmaybe absorbed; reducing the temperatureaof said element below saidvalue; reducing the pressure of said selected gas within said envelope;and introducing said one gas to said envelope to attain said givenpressure.

5. In association with an element having a temperature-dependentabsorbing characteristic for a selected gas in a particle acceleratorhaving an envelope and provided with first and secondtemperature-controlled gas-emitting and absorbing devices containing onegas and said selected gas, respectively, and in communication with saidenvelope, and said envelope normally containing said one gas, a methodof treating said element which comprises the steps of: heating saidfirst device to a gas-ab- "7 8 by to introduce saidlselected gas to saidenvelope of said References Cited in the file of this patent particleaccelerator; increasing the temperature of said UNITED STATES PATENTSelement-to avalue at which'said selected gas may be I L absorbed;reducing the temperature of said element be- 82036-5 Moore "77 May 1906low said value; reducing the temperature of said second 5 I 1,653,366; ff' 201 1927 .device to a gas-absorbing value within said operating 9Szlgetl O 1933 range thereby to remove an excess of said selected gas2O69495 f d 1937 from said envelope; heating said first device to a gas-Z126395 Journeaux 1938 emitting ternperature vvithin said operatingrange to in- P 1940 troduce said one gas to said envelope; and reducingthe 10 2285622' Sleplan June 1942 temperature of said first device belowsaid operating 2449838 Brett Sept' 1948 mm 2',497,91 1 Reilly n Feb. 21,1950

